The present invention relates to a toroidal-type continuously variable transmission that is used, for example, as a transmission mechanism of a vehicle.
Conventionally, as a transmission mechanism of a vehicle, there has been developed and used practically a toroidal-type continuously variable transmission.
Now, FIG. 6 shows the structure of a half-toroidal-type continuously variable transmission of a double cavity type. This toroidal-type continuously variable transmission comprises, within a housing 1, a first input disk 2a and a first output disk 3a respectively forming a first cavity la as well as a second input disk 2b and a second output disk 3b respectively forming a second cavity 1b. 
A pair of power rollers 5 is interposed between the first input and output disks 2a and 3a. The outer peripheral surfaces of the power rollers 5 are respectively contacted with the traction surfaces 4 of the respective disks 2a, 3a. Between the second input and output disks 2b, 3b as well, there are interposed a pair of power rollers 5, while the outer peripheral surfaces of these power rollers 5 are also respectively contacted with the traction surfaces 4 of the respective disks 2b, 3b. 
These power rollers 5 are rotatably mounted on their respective trunnions 7 by power roller bearings 6. The respective trunnions 7 can be swung about their associated trunnion shafts 8.
The traction surfaces 4 of the respective disks 2a, 2b, 3a, 3b are each formed as a concave-shaped surface which can be obtained by rotating an arc, the center of which is the trunnion shaft 8, about an axis extending at right angles to the trunnion shaft 8.
The first input disk 2a is mounted on an input shaft 10 in such a manner that it can be moved in the axial direction of the input shaft 10 with respect to the input shaft 10 while it is prevented against rotation by a ball spline 11.
The second input disk 2b is mounted on the input shaft 10 by a loading nut in such a manner that it is prevented against rotation by an involute spline 12. Therefore, the input disks 2a, 2b can be rotated integrally with the input shaft 10. This input shaft 10 can be driven or rotated by a drive source such as an engine.
The output disks 3a, 3b are interposed between the input disks 2a and 2b. The first output disk 3a is disposed opposed to the first input disk 2a, while the second output disk 3b is disposed opposed to the second input disk 2b. 
These output disks 3a, 3b are respectively supported on the input shaft 10 through bearings 13, 14 in such a manner that they can be rotated with respect to the input shaft 10. And, the output disks 3a, 3b are connected to each other by a connecting member 15 and can be rotated in synchronization with each other. On the connecting member 15, there is disposed an output gear 16.
On the back surface side of the first input disk 2a, there is disposed a hydraulic loading mechanism 20 of an oil pressure type. The loading mechanism 20 includes a hydraulic cylinder 21 that is mounted on the input shaft 10 in such a manner that it is opposed to the back surface of the input disk 2a. The peripheral wall 21a of the hydraulic cylinder 21 is fitted with the outer periphery of the input disk 2a in a liquid-tight manner through a seal member 22 in such a manner that it can be slid in the axial direction thereof. Between the hydraulic cylinder 21 and input disk 2a, there is formed a hydraulic chamber 25 having a closed structure.
The hydraulic cylinder 21 includes a fit cylinder 26 that is disposed in the center portion of the hydraulic cylinder 21 integrally therewith, while the input shaft 10 is fitted into the fit cylinder 26. And, there is formed an oil supply passage 27 which extends from an inner hole 10a formed in the input shaft 10 to the hydraulic chamber 25 within the hydraulic cylinder 21. That is, by means of the oil supply passage 27, oil can be pressure fed into the hydraulic chamber 25 through a control valve 29 from a hydraulic pump 28 serving as an oil supply member.
In addition, within the hydraulic chamber 25, there is disposed a countersunk spring 30 serving as pre-load applying means. When the countersunk spring 30 is viewed from the side surface thereof, it has a flat trapezoid shape. When it is viewed from the plane surface thereof, it has a circular ring shape.
This countersunk spring 30 is fitted with the outer periphery of the fit cylinder 26 of the hydraulic cylinder 21 and is interposed between the back surface of the input disk 2a and the inner surface of the hydraulic cylinder 21 with the plate section thereof inclined such that the inner peripheral edge thereof can be contacted with the back surface of the input disk 2a and the outer peripheral edge thereof can be contacted with the inner surface of the hydraulic cylinder 21. By the way, the countersunk spring 30 may also be disposed in such a manner that the inner peripheral edge thereof can be contacted with the back surface of the hydraulic cylinder 21 and the outer peripheral edge thereof can be contacted with the back surface of the input disk 2a. Due to the elastic force of the countersunk spring 30, there is applied such a preload that allows the respective disks 2a, 2b, 3a, 3b and their respective power rollers 5 to be elastically contacted with each other.
And, when the input shaft 10 and input disks 2a, 2b are rotated in linking with a drive source such as an engine, oil is supplied from the hydraulic pump 28 into the hydraulic chamber 25 through the control valve 29. Due to the oil pressure of the thus supplied oil, the first input disk 2a is pushed toward the first output disk 3a. Since a reaction force which the hydraulic cylinder 21 receives is applied to the input shaft 10, the second input disk 2b is pushed toward the second output disk 3b. 
The rotation power of the input disks 2a, 2b is transmitted through the power rollers 5 to the output disks 3a, 3b and, in linking with the output disks 3a, 3b, the output gear 16 is rotated.
To change the rotation speed ratio between the input shaft 10 and output gear 16, the respective power rollers 5 may be swung about their associated trunnion shafts 8. The swinging movements of the power rollers 5 change the contact positions between the peripheral surfaces of the power rollers 5 and the traction surfaces 4 of the disks 2a, 2b, 3a, 3b, thereby changing the rotation speed ratio between the input disks 2a, 2b and output disks 3a, 3b, that is, the rotation speed ratio between the input shaft 10 and output gear 16.
In order to enhance the power transmission efficiency of a transmission, it is important to secure a sufficient contact-pressure between the disks 2a, 2b, 3a, 3b and power rollers 5. In the present transmission, such contact pressure is secured by the oil pressure within the hydraulic chamber 25 as well as by the elastic force of the countersunk spring 30 within the hydraulic chamber 25.
The structure, in which, as described above, the countersunk spring 30 is incorporated into the hydraulic chamber 25 and the contact pressure between the disks 2a, 2b, 3a, 3b and power rollers 5 is secured by the oil pressure and the elastic force of the countersunk spring 30, is long known; for example, such structure is disclosed in U.S. Pat. No. 3,823,613.
In case where the countersunk spring 30 is incorporated in the hydraulic chamber 25, there is an advantage that the wear resistance of the countersunk spring 30 is enhanced, but there arises a problem that the presence of the countersunk spring 30 obstructs the flow of the oil within the hydraulic chamber 25.
That is, the circular-ring-shaped countersunk spring 30 is disposed within the hydraulic chamber 25 in the following manner that the inner peripheral edge of the countersunk spring 30 is contacted with the back surface of the input disk 2a and the outer peripheral edge thereof is contacted with the inner surface of the hydraulic cylinder 21, or, the inner peripheral edge of the countersunk spring 30 is contacted with the inner surface of the hydraulic cylinder 21 and the outer peripheral edge thereof is contacted with the back surface of the input disk 2a, while the plate section of the countersunk spring 30 is inclined between the inner surface of the hydraulic cylinder 21 and the back surface of the input disk 2a; and, in this state, the countersunk spring 30 presses against the input disk 2a elastically.
And, oil is supplied through the oil supply passage 27 into the inside area of the countersunk spring 30 within the hydraulic cylinder 21, and the oil then flows out into the outside area of the countersunk spring 30 within the hydraulic cylinder 21, thereby generating a given level of oil pressure.
However, since the inner peripheral edge of the spring 30 is contacted with the back surface of the input disk 2a and the outer peripheral edge thereof is contacted with the inner surface of the hydraulic cylinder 21, or, the inner peripheral edge of the spring 30 is contacted with the inner surface of the hydraulic cylinder 21 and the outer peripheral edge thereof is contacted with the back surface of the input disk 2a, there is formed only a slight clearance between them, so that the oil supplied into the inside area of the countersunk spring 30 is hard to flow out therefrom. As a result of this, the oil supplied into the interior of the hydraulic cylinder 21 suffers from a so called damping action, which delays the response characteristic between a hydraulic force to be controlled by the control valve 29 and a pressing force to be actually applied to the input disk 2a. Therefore, in case where torque is caused to vary suddenly, there is a fear that the pressing force can increase excessively to thereby degrade the oil flow efficiency or the pressing force can be short to thereby cause the input disk 2a to slip.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional toroidal-type continuously variable transmissions. Accordingly, it is an object of the invention to provide a toroidal-type continuously variable transmission in which, when oil is supplied into a hydraulic chamber, oil in the inside area of a countersunk spring can be made to flow smoothly into the outside area of the countersunk spring to thereby be able to raise the oil pressure of the whole of the hydraulic chamber up to a given level of oil pressure.
The above object can be attained by a toroidal-type continuously variable transmission according to the invention. The transmission comprises: an input disk and an output disk disposed such that they are disposed opposed to each other and are concentric with each other; power rollers swingably interposed between the input and output disks; and, a hydraulic loading mechanism of an oil pressure type for pushing the input disk toward the disposition side of the output disk to thereby transmit the rotation power of the input disk through the power rollers to the output disk, wherein the loading mechanism comprises: a hydraulic cylinder disposed on the back surface side of the input disk for defining a hydraulic chamber between the input disk and itself; an oil supply member for supplying oil into the hydraulic chamber to thereby push the input disk; a countersunk spring disposed in the hydraulic chamber and interposed between the back surface of the input disk and the inner surface of the hydraulic cylinder for elastically pushing the input disk toward the disposition side of the output disk; and, an oil flow passage which, when oil is supplied to the inside area of the countersunk spring disposed in the hydraulic chamber by the oil supply member, allows the oil in the inside area of the countersunk spring to flow smoothly into the outside area of the countersunk spring.
According to the invention, the oil flow passage may consist of a plurality of slits formed in the countersunk spring.
In addition, according to the invention, the oil flow passage may also consist of a plurality of circular-shaped through holes formed in the countersunk spring.
Further, according to the invention, the oil flow passage may also consist of a plurality of recessed grooves formed in the portion of the inner surface of a hydraulic cylinder that is to be contacted with the outer peripheral edge of a countersunk spring incorporated into the hydraulic chamber.
Furthermore, according to the invention, the oil flow passage may also consist of a plurality of recessed grooves formed in the portion of the inner surface of a hydraulic cylinder that is to be contacted with the inner peripheral edge of the countersunk spring incorporated into the hydraulic chamber.
Moreover, according to the invention, the oil flow passage may also consist of a plurality of recessed grooves formed in the portion of the back surface of the input disk that is to be contacted with the outer peripheral edge of a countersunk spring incorporated into the hydraulic chamber.
In addition, according to the invention, the oil flow passage may also consist of a plurality of recessed grooves formed in the portion of the back surface of the input disk that is to be contacted with the inner peripheral edge of the countersunk spring incorporated into the hydraulic chamber.